In manufacturing a semiconductor device, a large number of semiconductor wafers (hereinafter referred to as “wafers”), which are substrates, are held in a holder called a wafer boat in multiple stages and are loaded into a vertical processing container. A process gas is supplied from the side of the respective wafers and is converted into plasma to perform processing collectively. In the related art, there is known an apparatus that performs such plasma processing. Examples of this plasma processing include a film forming process using an ALD (Atomic Layer Deposition) process to form a SiO2 (silicon oxide) film or the like. In forming the SiO2 film, a step of supplying a source gas containing Si (silicon) to a wafer and causing the source gas to be adsorbed onto the wafer, and a step of converting an oxidizing gas for oxidizing the source gas adsorbed onto the wafer into plasma and supplying the active species of the oxidizing gas are repeatedly performed.
In addition to a product wafer from which a semiconductor device is manufactured, a monitoring wafer for monitoring how a film is formed on the product wafer is mounted on the wafer boat. A recess for forming a wiring of the semiconductor device is formed on the surface of the product wafer. However, the wiring is not formed on the surface of the monitoring wafer. Therefore, the recess is not formed on the monitoring wafer.
As for the products wafer, in order to increase the yield of the semiconductor device, it is required that a film be formed so as to increase the film thickness uniformity in the respective parts in a plane. When the film formation is performed with high film thickness uniformity in the respective parts in the plane of the product wafer as described above, from the viewpoint of grasping the film formation state of the product wafer, it is also required that a film be formed on the monitoring wafer so as to increase the film thickness uniformity in the respective parts in the plane.
As the recess is miniaturized, the surface area of the product wafer tends to increase. If the surface area increases, the active species of the process gas converted into plasma are not sufficiently spread to the plane of the product wafer. This may lead to a problem called micro-loading in which uneven processing is performed in the plane of the product wafer. In order to prevent this problem, it is considered to prolong the time for supplying the active species. That is to say, when forming the SiO2 film as described above, the active species of an O2 gas are supplied over a relatively long period of time.
If the supply time of the active species of the O2 gas is prolonged as described above, it is possible to form a SiO2 film with high film thickness uniformity in the respective parts in the plane of the product wafer. However, it was confirmed that the film thickness of the SiO2 film in the peripheral edge portion of the monitoring wafer becomes smaller than the film thickness of the SiO2 film in the central portion of the monitoring wafer. The reason why the film thickness becomes non-uniform in the plane of the monitoring wafer as described above may be as follows. The surface of each wafer subjected to the film forming process is in a charged state. Among the active species of the O2 gas supplied from the side of each wafer, ions opposite in polarity to the peripheral edge portion of the charged wafer are attracted to the peripheral edge portion of the wafer. By increasing the supply time of the active species as described above, a lot of ions are attracted to the peripheral edge portion of each wafer. Since the recess is not formed on the monitoring wafer, the amount of ions attracted and supplied per predetermined surface area of the monitoring wafer is larger than that of the product wafer. Thus, the modification of the SiO2 film proceeds greatly. As a result, it is considered that the film thickness in the peripheral edge portion of the monitoring wafer becomes smaller. As described above, there is a trade-off relationship between the film thickness uniformity in the plane of the product wafer and the film thickness uniformity in the plane of the monitoring wafer.
In the processing apparatus of the related art, the side peripheral wall of the processing container swells outward, thereby forming a protrusion portion that defines a vertically elongated space communicating with a processing space for accommodating a substrate holder and performing a process. An antenna for forming inductively coupled plasma in the vertically elongated space is provided on one of the left and right outer walls of the protrusion portion. A shield for shielding an electric field is provided on the front side of the antenna (at a position close to the processing space). However, even if the shield is disposed only on the front side of the antenna as described above, the action of the ions may not be sufficiently suppressed. Further, in another processing apparatus of the related art, there are provided a protrusion portion similar to that of the aforementioned apparatus of the related art, parallel flat plate type electrodes disposed to sandwich the protrusion portion from the left and right sides thereof and configured to form capacitively coupled plasma inside the protrusion portion, and shields disposed to sandwich the protrusion portion from the left and right sides thereof and configured to be position-adjustable back and forth. However, when forming the capacitively coupled plasma in such a manner, there is a concern that it is difficult to generate the active species in such an amount as to sufficiently spread to the wafer having a large surface area as described above.